JP2008103307A - Booster circuit, power supply device, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a heating time by lessening a switching loss at electromagnetic induction heating and heightening a peak value. <P>SOLUTION: The booster circuit is provided with an electric element structured of an inductance component boosting an inputted direct-current voltage up to a given voltage and electromagnetically inducing it to a load side, a capacity component, and a voltage resonance means using an electronic switch, and a heating coil having a boosting function capable of easily accelerating heating velocity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes a booster circuit that boosts a voltage to be supplied to electromagnetic induction heating means for heating an object to be heated by induction heating (IH), a power supply device including the booster circuit, and the power supply device. The present invention relates to a printer having an electrophotographic fixing device for fixing a developer image transferred to a sheet of paper, a copying machine, a facsimile machine, and an image forming apparatus including a composite machine thereof.

Conventionally, there has been an electromagnetic induction heating device that is driven by a commercial AC voltage and does not break even when a surge voltage such as lightning, a momentary power failure, a voltage drop, or a rise occurs (see, for example, Patent Document 1). .
In the voltage resonance circuit of such an electromagnetic induction heating device (IH device), a voltage Q times is generated.
The quality factor (Quality factor: Q) is used as a standard indicating the goodness of the voltage resonance circuit, and includes the frequency ω ₀ of the voltage resonance circuit, the inductance L of the coil, the capacitance C of the capacitor, and the equivalent resistance thereof. Assuming that the resistance value is R, Q is obtained by arithmetic processing according to the following equations (A) and (B).
(A) Q = ω ₀ L / R
(B) Q = 1 / R · 1 / ω ₀ C
For example, during series resonance, the voltage of the coil or capacitor becomes Q times the power supply voltage.

  On the other hand, an insulated gate bipolar transistor (IGBT) is often used as an electronic switch that performs switching of relatively large power.

FIG. 14 is a diagram showing a circuit configuration of the IGBT, and FIG. 15 is a diagram showing an output waveform of each terminal of the IGBT when 1200 W of electric power is input to the IGBT during electromagnetic induction heating driving.
As shown in FIG. 14, the IGBT is a bipolar transistor in which a MOS type FET (Metal Oxide Field Effect Transistor: MOSFET) 110 is incorporated in the gate portion, and is driven by a voltage between the gate terminal G and the emitter terminal E. It is a self-extinguishing type that can be turned on and off by a signal, and is a semiconductor element capable of switching high power.
As shown in FIG. 15, the voltage 112 at the gate terminal G and the voltage 113 at the collector terminal C change with respect to the input voltage 111.
However, the IGBT can switch a relatively large power as compared with the FET, but the switching speed is relatively slow.

For example, when electromagnetic induction heating (IH) is used for fixing an image in an image forming apparatus, a field effect transistor (Field Effect Transistor: FET) used in a normal switching power supply is used to perform a large current switching with a withstand voltage of 1000 V and a current of 60 A. Then, it becomes impossible high power switching.
Therefore, the IGBT is often used.
JP 2004-266890 A

As a method for shortening the heating time in the conventional electromagnetic induction heating device, there is a method of increasing the induction electromotive force of electromagnetic induction. One method is to increase the resonance voltage.
In the coil configuration for electromagnetic induction heating in the conventional electromagnetic induction heating device, in order to increase the resonance voltage, the peak value of the resonance voltage (referred to as “resonance peak value”) can be increased only by changing the inductance component or the capacitor component. be changed.
By the way, in order to increase the resonance peak value, the resonance time may be shortened. However, the IGBT of the electronic switch used for electromagnetic induction heating has a problem in that the upper limit of the switching speed is limited and switching cannot be performed quickly.
In addition, if the switching speed is forcibly increased, the switching loss increases.
Furthermore, increasing the resonance wave height value, that is, the Q value has a problem that the sharpness of the waveform also increases, and the Q changes even with a slight frequency change, making control difficult.

FIG. 16 is a diagram showing output waveforms of each terminal of the IGBT during electromagnetic induction heating drive.
(A) of the same figure is an example of a waveform when the resonance period is long and resonance is not realized, and noise is generated in the overlapping portion and loss is large.
(B) of the figure is a state where resonance is realized, and is a waveform example in the case of efficient driving.
(C) in the figure shows that resonance is realized, but the resonance period is short, the resonance period is short, the waveform sharpness is high, and control is difficult. Further, this is a waveform example when a large voltage is applied to the coil and heat is generated and loss is large, and the current flows to the body diode of the IGBT and current is large and loss is large.

As described above, in the conventional current induction heating device, in order to increase the induced electromotive force and increase the heating rate, if the value of Q is increased, the sharpness of the resonance waveform increases and control becomes difficult. It was.
The present invention has been made in view of the above points, and an object of the present invention is to reduce the switching loss in electromagnetic induction heating and increase the resonance wave height to shorten the heating time of the object to be heated.

In order to achieve the above object, the present invention provides the following booster circuit, power supply device and image forming apparatus.
(1) A means for generating a pseudo-high frequency AC voltage from a DC voltage, and a magnetic line of force is generated by applying a pseudo-high frequency AC voltage generated by the means, and the object to be heated is electromagnetically heated based on the magnetic line of force. A resonance capacitor is provided in parallel with the coil, and the coil is configured by a Japanese-electrically connected electromagnetic induction coil and the resonance coil, and the pseudo coil is connected to the electromagnetic induction coil. A step-up circuit provided with switch means for switching between a state in which a high-frequency AC voltage is applied and a state in which the pseudo-high-frequency AC voltage is applied to the resonance capacitor.

(2) In the booster circuit as described above, a booster circuit provided with means for correcting a deviation in inductance of the electromagnetic coupling coil.
(3) In the booster circuit as described above, a booster circuit provided with means for controlling the value of the pseudo high frequency so as to bring the magnetic coupling coil into a resonance state.
(4) A power supply device including the booster circuit as described above.
(5) A power supply apparatus provided with a rectifier circuit that rectifies the DC voltage to generate the DC voltage.
(6) An image forming apparatus including the power supply device as described above.

(7) A switch that generates a pseudo-high frequency AC voltage from a DC voltage, a first coil that electromagnetically heats the object to be heated based on a line of magnetic force generated by a change in current caused by the application of the AC voltage, and a first coil And a capacitor connected in parallel with the first coil and the second coil with respect to the switch.
(8) In the booster as described above, the switch is a booster circuit that is an insulated gate bipolar transistor.
(9) In the booster as described above, a booster circuit provided with a control unit for correcting a deviation in inductance between the first coil and the second coil.
(10) In the boosting device as described above, a boosting circuit provided with means for switching the switch at a frequency near the resonance frequency of the first coil, the second coil, and the capacitor.

(11) A DC voltage source and a booster circuit, wherein the DC voltage source generates a DC voltage, and the booster circuit generates a pseudo high-frequency AC voltage from the DC voltage generated by the DC voltage source. A first coil that electromagnetically heats the object to be heated based on a line of magnetic force generated by a change in current due to the application of the AC voltage, a second coil that is connected in Japanese with the first coil, and A power supply device having a capacitor connected in parallel with the first coil and the second coil with respect to the switch.

(12) a rectifier circuit and a booster circuit, wherein the rectifier circuit rectifies an AC voltage to generate a DC voltage, and the booster circuit generates a pseudo-high frequency AC voltage from the DC voltage generated by the rectifier circuit. A switch to be generated, a first coil for electromagnetically heating an object to be heated based on a line of magnetic force generated by a change in current caused by the application of the AC voltage, and a second coil connected in Japanese with the first coil And a capacitor connected to the switch in parallel with the first coil and the second coil.
(13) An image forming apparatus comprising the power supply device as described above, wherein the heated member of the power supply device is a fixing roller for fixing the toner image on the recording medium to the recording medium.

  The booster circuit, the power supply device, and the image forming apparatus according to the present invention can reduce the switching loss in electromagnetic induction heating and increase the resonance peak value to shorten the heating time of the object to be heated.

Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.
First, a general electromagnetic induction heating system will be described before describing the embodiment of the present invention.
FIG. 11 is a block diagram showing a functional configuration of a general electromagnetic induction heating system which is a reference of the present invention.
The electromagnetic induction heating system 90 is an IH cooking heater. Below the top plate (not shown) of the IH cooking heater, there is a heating coil 94. By the heating coil 94, a pan 95 (a pan made of iron, aluminum, stainless steel, etc.) is heated. The case where water is heated by electromagnetic induction heating will be described.

When the electromagnetic induction heating system 90 is turned on, an alternating current flows through the heating coil 94 under the top plate. This alternating current is a pseudo high frequency, approximately 20 KHZ, and at most several tens of kHz.
The pseudo high frequency is rectified by a rectifier 92 from a commercial power source 51 of AC 100 V having a commercial frequency of 60 Hz or 50 Hz by a high frequency inverter 93 which is an inverter power source to generate a direct current and is supplied to the high frequency inverter 93.

The high-frequency inverter 93 generates a high-frequency alternating current from the direct current and passes it through the heating coil 94. When a current flows through the heating coil 94, magnetic lines of force are generated so as to surround the heating coil 94. Due to the magnetic lines of force, a current called eddy current flows in the pan 95 near the heating coil 94. In DC, eddy current is generated only for a moment when the power is turned on.
The eddy current is Joule heat loss. In addition, there is hysteresis loss, but it is a negligible level. Further, an eddy current in the direction opposite to the current of the heating coil 94 is also generated.
In this way, the pot bottom itself generates heat due to the eddy current generated at the bottom of the pot 95 of the object to be heated. This is why it is called direct heating. The calorific value at that time can be obtained based on the following equation.

Calorific value W = I ² × R (I: eddy current, R: electrical resistivity at the bottom of the pan)
The self-heating heat at the bottom of the pan is transferred to the water in the pan 95, so that the water in the pan 95 is warmed and becomes hot water.
In addition, the electromagnetic induction heating system as described above has recently been adopted in OA equipment. For example, in an image forming apparatus including a copying machine, a halogen heater or the like has been conventionally used in a toner fixing process. By using an electromagnetic induction heating system, fine temperature control is possible and it is effective for energy saving such as shortening the start-up time.

FIG. 12 is a block diagram showing a functional configuration of an electromagnetic induction heating device as a premise of the present invention.
The basic operation of electromagnetic induction heating in this electromagnetic induction heating apparatus 1 ′ will be described.
(1) AC100V (commercial voltage) of the commercial power source 4 is directly rectified by the rectifier circuit 2 to create DC141V.
(2) DC141V is converted into 600V _0-p , 50A _0-p , 20KHZ to 40KHZ by an inverter circuit 3 ′ having an electromagnetic induction heating control unit (IH control unit (also referred to as “microcomputer control unit”)) 6 and a drive circuit 7. The pseudo high frequency voltage is converted.

(3) The inverter circuit 3 'uses an IGBT 5 which is a switching element capable of high power switching.
(4) The IH control unit 6 turns the IGBT 5 on and off via the drive circuit 7.
(5) The operation of the above (4) is voltage resonance.
(6) The diode D1 is a body diode of the IGBT 5.
(7) The IH control unit 6 performs IH control, and performs resonance point tracking control, current protection, and voltage protection.

Next, the phenomenon of electromagnetic induction heating will be described in detail in a little later order.
FIG. 13 is a diagram for explaining the principle of electromagnetic induction heating.
(1) When an alternating current is supplied from the power source 101 to the coil 100, a magnetic field is generated by the coil current flowing in the coil 100.
(2) When a magnetic field is generated in the coil 100, a magnetic field is also generated in the metal cylinder 102 that is an object to be heated in the coil 100.
(3) A current (this is called “eddy current”) flows in the metal cylinder 102 in such a direction as to cancel the magnetic field. The closer the eddy current is to the surface of the metal cylinder 102, the more current flows (in this way, when a high-frequency current flows through a conductor, the current density is high on the surface of the conductor and decreases when the surface is separated from the surface. "The higher the frequency, the more current is concentrated on the surface, so the AC resistance of the conductor increases).

(4) Joule heat is generated by the eddy current and the electric resistance of the metal cylinder 102. At that time, the closer to the surface of the metal cylinder 102, the greater the current, and the greater the amount of heat generated.
(5) The temperature of the metal cylinder 102 gradually increases from the surface, but at the same time, heat dissipation starts.
(6) The central portion of the metal cylinder 102 receives heat conduction generated near the surface and is heated with a slight delay from the surface.

〔Example〕
Next, an embodiment of the image forming apparatus of the present invention will be described.
FIG. 2 is a sectional view conceptually showing the configuration of an electrophotographic image forming apparatus according to an embodiment of the present invention. A fixing device using electromagnetic induction heating by a booster device and a power supply device according to the present invention is shown. Adopted.
The image forming apparatus mainly includes a reading unit 11 for reading a document, an image forming unit 12 for forming an image, an automatic document feeder (ADF) 13, a document discharge tray 14 for stacking documents sent from the ADF 13, and a paper feed cassette. The paper feeding unit 19 includes 15 to 18 and the paper discharge unit (discharge tray 20) for stacking recording paper.

Then, when the document D is set on the document table 21 of the ADF 13 and the user performs an operation on an operation unit (not shown), for example, when the user presses the print key, the uppermost document D rotates the pickup roller 22. Thus, the sheet is fed in the direction of arrow B1, and is fed onto the contact glass 24 fixed to the reading unit 11 by the rotation of the document conveying belt 23, and stops there.
The image of the document D placed on the contact glass 24 is read by a reading device 25 located between the image forming unit 12 and the contact glass 24.

The reading device 25 includes a light source 26 that illuminates the document D on the contact glass 24, an optical system 27 that forms an image of the document, a photoelectric conversion element 28 that includes a CCD that forms an image of the document, and the like.
After the image reading is completed, the document D is transported in the direction of the arrow B2 by the rotation of the document transport belt 23 and discharged onto the discharge tray 14.
In this way, the document D is fed one by one onto the contact glass 14 and the document image is read by the reading unit 11.

On the other hand, inside the image forming unit 12, a photoconductor 30 as an image carrier is disposed.
The photosensitive member 30 is driven to rotate clockwise in the drawing, and the surface is charged to a predetermined potential by the charging device 31.
Further, the writing unit 32 emits a laser beam L that is light-modulated in accordance with image information read by the reading device 25, and the surface of the charged photoreceptor 30 is exposed with the laser beam L, whereby the photoreceptor is exposed. An electrostatic latent image is formed on the surface 30.

When the electrostatic latent image passes through the developing device 33, the electrostatic latent image is transferred to the recording medium P fed between the photosensitive member 30 and the transfer device 34 by the opposing transfer device 34. The surface of the photoconductor 30 after the toner image is transferred is cleaned by a cleaning device 35.
A plurality of paper feed cassettes 15 to 18 disposed below the image forming unit 12 contain recording media P such as paper, and the recording media P is fed from any of the paper feed cassettes 15 to 18 in the direction of arrow B3. The toner image formed on the surface of the photoreceptor 30 as described above is transferred onto the surface of the recording medium P.

Next, the recording medium P is passed through the fixing device 36 in the image forming unit 12 as indicated by an arrow B4, and the toner image transferred to the surface of the recording medium P by the action of heat and pressure is fixed.
The recording medium P that has passed through the fixing device 36 is conveyed by the discharge roller pair 37, discharged to the discharge tray 20 as indicated by an arrow B5, and stacked.
The fixing device 36 includes a fixing roller 40 that is a heat generating roller that is heated by electromagnetic induction of the electromagnetic induction heating device 1, a pressure roller 41 that is arranged so that the axis of the fixing roller 40 is parallel to the fixing roller 40, and the like.

The fixing roller 40 is made of, for example, a metal hollow cylindrical magnetic metal member containing iron, cobalt, nickel, or an alloy thereof, and preferably has a low heat capacity and a high temperature rise. Of course.
In addition, the fixing roller 40 is configured, for example, by covering a metal core made of magnetic metal with heat-resistant silicone rubber in a solid or foamed form.
On the other hand, the pressure roller 41 is configured by, for example, providing an elastic member having high heat resistance and high toner releasability on the surface of a metal core made of a metal cylindrical member containing copper or aluminum having high thermal conductivity. .
A metal containing stainless steel may be used for the core metal.
The fixing roller 40 and the pressure roller 41 described above form a nip portion in which a contact portion during rotation passes through a recording medium on which unfixed toner is placed and is pressed and heated.

FIG. 1 is a circuit diagram showing an internal configuration of the electromagnetic induction heating device 1 shown in FIG.
The electromagnetic induction heating device 1 includes a rectifier circuit 2 and an inverter circuit 3, and is disposed in the fixing device 36 with a gap between the magnetic coupling coil L 1 and the fixing roller 40 that is a heated body. .
The rectifier circuit 2 includes a commercial power source 4, a smoothing filter coil L2, a noise filter capacitor C, a capacitor C2, a current transformer CT, and the like.
The smoothing filter coil L2 and the capacitor C2 constitute an LC filter.
The smoothing filter coil L2 and the capacitor C2 constitute a low-pass filter.
The rectifier circuit 2 converts a 100 V (50 HZ / 60 HZ) AC voltage of the commercial power source 4 into a direct current (DC) voltage of about 141 V and supplies the converted voltage to the inverter circuit 3.
The current transformer CT is for detecting the current of the commercial power supply 4. Here, the current of AC 100 V is detected, and if there is an abnormality, the protection circuit is activated.

The inverter circuit 3 includes a magnetic coupling coil L1 configured by a Japanese-electrically connected electromagnetic induction coil and a resonance coil, a resonance capacitor C1, a switching element IGBT5, and a body diode (built-in diode) D1 of the IGBT5. And an electromagnetic induction heating control unit (IH control unit) 6 realized by a microcomputer including a CPU, a ROM, a RAM, and the like, and a drive circuit 7.
The magnetic coupling coil L1 has a coil connection between the coil La and the coil Lb, and serves as a heating coil by the coil Lb and a resonance coil by the coils La and Lb.

In the resonance capacitor C1, the energy at the time of resonance due to switching of the IGBT 5 is 1 / 2Li ^ 2 = 1 / 2CV ^ 2 (^: exponent, L: inductance, i: current, C: capacitance, V: voltage). .
The IGBT 5 is switch means for converting a DC voltage into a pseudo high frequency AC voltage.
The IH control unit 6 functions as means for correcting the deviation of the inductance of the electromagnetic coupling coil L1, and the IH control unit 6 and the drive circuit 7 set the pseudo high frequency value of the IGBT 5 so that the magnetic coupling coil L1 is in a resonance state. Serves as a means to control

The IH control unit 6 includes an oscillator (timer) (not shown), a protection circuit, and the like, and sends an instruction to the drive circuit 7 at the switching timing of the IGBT 5.
The drive circuit 7 is a circuit typified by a totem pole circuit, and controls driving for switching ON / OFF switching of the IGBT 5 based on an instruction from the IH control unit 6.
This inverter circuit 3 makes the DC voltage supplied from the rectifier circuit 2 pseudo-high frequency (for example, 20 KHZ to 60 KHZ) by the IGBT 5, and switches the ON / OFF switching of the IGBT 5 by the control of the IH control unit 6 and the drive circuit 7. Then, a pseudo high frequency is supplied to the magnetic coupling coil L1 and the resonance capacitor C1, and the fixing roller 40 is electromagnetically heated by generation of a magnetic field of the magnetic coupling coil L1 and resonance of the resonance capacitor C1.
The fixing roller 40 is efficiently heated by the configuration of the resonance circuit including the magnetic coupling coil L1, the resonance capacitor C1, and the switching element IGBT 5 shown in FIG.

The electromagnetic induction heating device 1 performs a high-efficiency switching operation by performing a resonance operation with a good Q value by causing the IGBT 5 to perform a switching operation in the vicinity of the resonance frequency f shown in Equation 1. First, when the IGBT 5 is ON, a coil current flows through the magnetic coupling coil L1, and when the IGBT 5 is OFF, a resonance voltage is applied to the resonance capacitor C1.
When a current flows to the magnetic coupling coil L1, an eddy current flows to the fixing roller 40, and the power of i ^ 2R (R: resistance) is generated by the eddy current and the metal resistance of the fixing roller 40. Joule heat is generated and the fixing roller 40 is heated.

This electromagnetic induction heating device 1 is characterized by the configuration of the magnetic coupling coil L1. The magnetic coupling coil L1 has both functions of a voltage resonance coil and a heating coil for the fixing roller 40, and has no role as the smoothing filter coil L2 after rectifying AC100V by the rectifier circuit 2. Different.
Electromagnetic induction heating can be performed, for example, at AC 100 V, 60 Hz / 50 Hz, but for faster heating, it is realized by increasing the voltage and frequency.

For example, an input AC of 100V, 60HZ / 50HZ is raised to an output of about 600-1000V _0-p , 20 KHZ to 40 KHZ.
For this purpose, an inverter circuit 3 is provided.
The inverter circuit 3 has a resonance waveform that is Q times the DC voltage from the rectifier circuit 2 by a voltage resonance circuit (also referred to as “LC resonance circuit”) that includes a magnetic coupling coil L1 that is a resonance and heating coil and a resonance capacitor C1. Can be made.
The electromagnetic induction heating apparatus 1 of this embodiment has a coil configuration using boosting means and a summing connection that does not affect the resonance frequency or Q in terms of cost.

In this way, the magnetic coupling coil L1 serves as a heating coil and a resonance coil, and the inductance value cannot be changed greatly.
Therefore, since the eddy current of the fixing roller 40 is increased by increasing the pressure without changing the inductance value, the switching loss of the IGBT 5 can be reduced, the crest value can be increased, and the heating time can be shortened.
Thus, by using the coil configuration for the electromagnetic induction heating means, the object to be heated can be easily and efficiently heated in a short time without changing the resonance frequency.

Next, the coil having both the heating function and the resonance function using the above-described summing connection will be further described.
FIG. 3 is a circuit diagram of a heating coil in which a plurality of coils are connected in Japanese.
(A) of the figure is a structural example of a magnetic coupling coil having both the heating and resonance functions using the above-described summing connection, and (b) of the same figure is a structural example of a conventional heating coil. It is.
In the magnetic coupling coil shown in FIG. 2A, the amount of heat generated is determined by the induced electromotive force per one turn of the coil.
Here, in the conventional heating coil shown in FIG. 5B, when e = induced electromotive force, N = number of turns, L = inductance, φ = magnetic flux, and I = current, induced electromotive force e = −N · Δφ / Δt, induced electromotive force e = −L · ΔI / Δt, and inductance L = N · Δφ / ΔI, and the induced electromotive force e is directly proportional to the number of turns N and the inductance L.

Therefore, in order to increase the amount of heat generated by increasing the induced electromotive force per one time, the number of windings may be increased, but this also changes the inductance.
Since the conventional electromagnetic induction heating device is driven by providing a resonance circuit of a heating coil and a capacitor as shown in (b) of the figure, when the inductance is changed, the frequency is changed as shown in Equation 1 above. It will fluctuate. And if it deviates significantly from this resonance frequency, drive efficiency will fall remarkably.

On the other hand, in the magnetic coupling coil shown in FIG. 5A, when M = mutual inductance and k = coupling coefficient, two coils La are obtained from the arithmetic expression shown in Equation 2 and e2 = −M · ΔI / Δt. And the inductance determined by Lb, the induced electromotive force is determined regardless of the number of turns, so that the dielectric electromotive force can be easily controlled without a decrease in efficiency.
Also, with such a coil configuration, it is possible to boost n times the La: Lb inductance ratio without changing the inductance value, and to increase the induced electromotive force.
Furthermore, since the structure does not become complicated as in the case of an insulating transformer, the circuit can be manufactured at low cost.

According to the electromagnetic induction heating device 1 as described above, since the fixing roller 40 is rapidly heated to a target temperature, Q is about 5 to 7 times (in the case of one stone drive).
Here, the LC resonance circuit is driven with high efficiency by driving in the vicinity of f ₀ .
FIG. 4 is a waveform diagram showing an example of changes in impedance and Q in the LC resonance circuit.
(A) of the figure shows the impedance of the heating coil, and (b) of the figure shows Q (Quality factor).
Once the LC constant is determined by the LC resonance circuit, the resonance frequency is determined from Equation 1, and the drive frequency is determined. Heating (energy) is determined by the electromagnetic flux. Furthermore, the electromagnetic flux is determined by the current flowing in the metal. The current is determined by the IGBT's _Vce0-p and the metal resistance value.

Here, a reference technique of the heating coil will be described.
5 to 7 are diagrams showing the configuration of the heating coil according to the reference technique of the present invention.
FIG. 5 shows a circuit configuration comprising a heating coil 50, IGBTs 51 and 52, a resonance capacitor 53, etc. for heating the fixing roller 40 ′ as a heated body, and FIG. 6 heats the fixing roller 40 ′ as the heated body. 7 shows a circuit configuration including a heating coil 60, IGBTs 61 to 63, diodes D2 to D5, a resonance capacitor 64, and the like. FIG. 7 shows a heating coil 70, an IGBT 71, and a resonance capacitor 72 for heating the fixing roller 40 'as a heated body. The circuit configuration which consists of diode D6 is shown.
In each circuit in each of the above-described drawings, if the inductance L of each heating coil is increased or the capacitance C is decreased, the magnetic field generated in the metal cylinder of the heating coil and the eddy current flowing in the direction to cancel the magnetic field. The value of Q can be increased.

However, the resonance frequency f ₀ also changes due to the magnetic field generated by the current flowing in each heating coil. At this time, if the limit speed of the IGBT is exceeded, the power loss during switching also increases.
Also, increasing Q is very difficult in view of controlling the resonance waveform to be sharp. It is also conceivable that the step-up ratio changes greatly if the frequency moves even a little.
Furthermore, increasing the value of the inductance L of the heating coil is limited due to space limitations.
Here, as a method of increasing the resonance voltage V _ce0-p without changing the Q, a method of increasing the resonance voltage by applying a DC bias to the resonance voltage and putting on clogs, for example, using an electric double layer capacitor or the like There is. However, in addition to the power source for supplying power to the electromagnetic induction heating device, a charge / discharge power source for the capacitor is required, which increases the cost.

FIG. 8 is a circuit diagram showing an example of a heating coil configured by a plurality of coils in a Japanese-style connection. The heating coil Lc and a smoothing filter coil Ld are connected in a Japanese-style connection.
FIG. 9 is a circuit diagram for electromagnetic induction heating using the heating coil shown in FIG. This is a circuit configuration in which the heating coil Lc and the smoothing filter coil Ld shown in FIG.
FIG. 10 is a circuit diagram showing another configuration example of a circuit for electromagnetic induction heating using the heating coil shown in FIG. In this circuit, a resonance capacitor 81 is provided in the circuit configuration shown in FIG.

For the circuits shown in FIGS. 9 and 10, respectively, L0 = Lc + Ld + 2M, and in each equation of Equation 3, when the inductance of Ld is 1, the inductance of Lc is (1 / n) ^{2. In} this case, the coupling coefficient M is Therefore, when Lc + Ld + 2M = L0 is expressed as Ld inductance 1, (1 / n) ² +1 ² + 2 × 1 / n = (1 + 1 / n) ² , and the values of Lc and Ld are Ld = L0 × 1 / (1 + 1 / n) ² , Lc = L0 × 1 / (1 + 1 / n) ² × (1 / n) ²
If this coil configuration is used, the voltage can be boosted n times with the inductance ratio Lc: Ld without changing the value of the inductance L.

  The booster circuit, the power supply device, and the image forming apparatus according to the present invention can be applied to all devices for heating a heated object.

It is a circuit diagram which shows the internal structure of the electromagnetic induction heating apparatus 1 shown in FIG. 1 is a sectional view conceptually showing the structure of an electrophotographic image forming apparatus as an embodiment of the present invention. It is a circuit diagram of a heating coil in which a plurality of coils are connected in Japanese. It is a wave form diagram which shows the example of a change of the impedance and Q in LC resonance circuit. It is a figure which shows the structure of the heating coil of the reference technique of this invention.

It is a figure which similarly shows the structure of the heating coil of the reference technique of this invention. It is also a figure showing the composition of the heating coil of reference technology of this invention. It is a circuit diagram which shows an example of the heating coil comprised by carrying out Japanese-style connection of several coils. FIG. 9 is a circuit diagram for electromagnetic induction heating using the heating coil shown in FIG. 8. It is a circuit diagram which shows the other structural example of the circuit for electromagnetic induction heating using the heating coil shown in FIG.

It is a block diagram which shows the function structure of the general electromagnetic induction heating system used as the reference of this invention. It is a block diagram which shows the function structure of the electromagnetic induction heating apparatus used as the premise of this invention. It is a figure where it uses for description of the principle of electromagnetic induction heating. It is a figure which shows the circuit structure of IGBT. It is a figure which shows the output waveform of each terminal of IGBT when the electric power of 1200W is input into IGBT at the time of electromagnetic induction heating drive. It is a figure which shows the output waveform of each terminal of IGBT at the time of electromagnetic induction heating drive.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1 ': Electromagnetic induction heating device 2: Rectification circuit 3, 3': Inverter circuit 4: Commercial power supply 5: IGBT 6: IH control part 7: Drive circuit 11: Reading unit 12: Image formation part 13: ADF 14: Document discharge trays 15 to 18: Paper feed cassette 19: Paper feed unit 20: Paper discharge tray 21: Document tray 22: Pickup roller 23: Document transport belt 24: Contact glass 25: Reading device 26: Light source 27: Optical system 28 : Photoelectric conversion element 30: Photoconductor 31: Charging device 32: Writing unit 33: Development device 34: Transfer device 35: Cleaning device 36: Fixing device 37: Discharge roller pair 40, 40 ′: Fixing roller 41: Pressure roller

Claims (13)

Means for generating a pseudo-high frequency AC voltage from the DC voltage, and a coil for generating magnetic lines of force by applying the pseudo-high frequency AC voltage generated by the means, and electromagnetically heating the object to be heated based on the lines of magnetic force; A resonance capacitor is provided in parallel with the coil, and the coil is configured by a Japanese-style connection of an electromagnetic induction coil and a resonance coil, and the pseudo-high frequency alternating current is connected to the electromagnetic induction coil. A booster circuit comprising switch means for switching between a state in which a voltage is applied and a state in which the pseudo-high frequency AC voltage is applied to the resonance capacitor. 2. The booster circuit according to claim 1, further comprising means for correcting a deviation in inductance of the electromagnetic coupling coil. 3. The booster circuit according to claim 1, further comprising means for controlling the value of the pseudo high frequency so as to bring the magnetic coupling coil into a resonance state. A power supply apparatus comprising the booster circuit according to claim 1. 5. The power supply apparatus according to claim 4, further comprising a rectifier circuit that rectifies and generates the DC voltage. An image forming apparatus comprising the power supply device according to claim 4. A switch that generates a pseudo-high frequency AC voltage from the DC voltage;
A first coil that electromagnetically heats an object to be heated based on magnetic lines generated by a change in current caused by application of the AC voltage;
A second coil that is Japanese-electrically connected to the first coil;
A booster circuit comprising a capacitor connected in parallel to the first coil and the second coil with respect to the switch.   8. The booster circuit according to claim 7, wherein the switch is an insulated gate bipolar transistor.   9. The booster circuit according to claim 7, further comprising a control unit that corrects a deviation in inductance between the first coil and the second coil.   10. The booster circuit according to claim 7, further comprising means for switching the switch at a frequency in the vicinity of a resonance frequency of the first coil, the second coil, and the capacitor. A DC voltage source and a booster circuit;
The DC voltage source generates a DC voltage;
The booster circuit electromagnetically heats a heated object based on a switch that generates a pseudo-high frequency AC voltage from a DC voltage generated by the DC voltage source and a magnetic field generated by a change in current caused by the application of the AC voltage. A first coil; a second coil that is connected in harmony with the first coil; and a capacitor connected in parallel with the first coil and the second coil with respect to the switch. A featured power supply. A rectifier circuit and a booster circuit;
The rectifier circuit rectifies an AC voltage to generate a DC voltage,
The booster circuit performs electromagnetic induction heating of the object to be heated based on a switch that generates a pseudo-high frequency AC voltage from the DC voltage generated by the rectifier circuit, and magnetic lines generated by a change in current caused by application of the AC voltage. And a capacitor connected in parallel with the first coil and the second coil with respect to the switch. Power supply. A power supply device according to claim 11 or 12,
The image forming apparatus according to claim 1, wherein the heated body of the power supply device is a fixing roller that fixes the toner image on the recording medium to the recording medium.

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